Hmm.. so, you cd into the directory that has gconvert executable, and then run it and it doesn't work and gives you that output? As you may have probably already guessed, Windows can't find the program name that you are typing. When program names are run from the command line Windows will check directories in the %PATH% variable (try set path at cmd prompt) and also the current directory. The error suggests the file wasn't found in either.
In this sort of weird situation I do what I call a 'Reality Check'. You would individually check things such as "Is the executable file being typed (spelled) correctly? Am I actually in the directory where the executable lives? Is the executable actually there? Sounds like dumb simple things but when your mind is racing, the little stuff is very easy to overlook. I like to joke that big problems often have simple solutions because the solution is something dumb like actually typing in the right path or filename, rebooting, or just plain turning it on. It happens to me more that I would like to admit.
Probably many of us.
The error suggests no problem with gconvert, it's just not being found. I could convert these graphics for you if you'd like but I would like for you to supply the gconvert .xml file otherwise I would need to create it and I may not have your best intentions in mind.
Other than the graphics being .bmp (should be .png, its easier that way) your graphics and dimensions appear valid.
What are you doing to try to run gconvert? Are you doing something like this?:
Example to get to the gconvert directory:
cmd (from start>run)
C:\Users\username\ (should be the directory you start at.)
cd desktop
cd uzebox
cd bin
(now you should be in the bin directory.)
dir (type this and see if gconvert is in the list of files)
If gconvert isn't there then check to make sure that you are in the correct directory for the binary files. I'll assume that you obtained them from the old r212 trunk.)
Just running "gconvert" should give you some sort of output.